Canning and Fish Packaging Technology

Unit 3 - Unit operations in canning

3.2.3.1.Exhausting of filled cans
The importance of removal of air from the cans after filling the food was realized by canning experts from the very beginning. Even in historical days of canning, it was thought that the contact of air with food was responsible for the spoilage and if the air was removed, food could be preserved for long time after heat processing.

Even the famous chemist Gay Lusac thought in the same way. However, if air is not removed from the can while sealing, it would expand during heat processing and can ends (lids) become permanently convex and it would be rejected thinking that the food inside was spoilt. Also, due to high pressure inside the can, seam would get loosened and entry of air and bacteria may take place and spoil the product. Hence, it is essential to exhaust the can prior to sealing.